There is a memory device in which memory cells are three-dimensionally aligned by forming a memory hole in a stacked body where a plurality of electrode layers functioning as control gates in the memory cells and a plurality of insulating layers are alternately stacked, forming a charge storage film on a side wall of the memory hole, and then providing silicon serving as a channel in the memory hole.
In this type of memory device, there is a U-shaped memory string structure that includes: a pair of columnar parts extending in a stacking direction of the stacked body including a plurality of electrode layers; and a coupling part embedded in a back gate and connecting the pair of columnar parts.
Before the formation of the stacked body including the electrode layers, a concave portion (a space portion) is formed in a foundation layer serving as the back gate, and a sacrifice film is embedded in the concave portion. After that, a stacked body including sacrifice layers formed between each of the plurality of electrode layers and each of the plurality of electrode layers is formed on the foundation layer and then, a hole of the columnar part is formed, and the sacrifice film in the concave portion and the sacrifice layers are selectively removed through the hole by etching. After that, a charge storage film and a channel body layer are formed in the hole, in the concave portion and between the plurality of electrode layers, and thus the nonvolatile semiconductor memory device is formed.
However, each of the plurality of electrode layers contains an impurity element. When the impurity element diffuses to the sacrifice layers during the manufacturing process, the sacrifice layers may not be sufficiently removed by etching. Furthermore, data retention may degrade due to an electric field generated at an edge portion of the electrode layer.